See Section 27.6.2 for isosceles triangles in space.
The isosceles_triangle command creates isosceles triangles.
With the argument var, c will be assigned to var.
| isosceles_triangle(i,1,-3*pi/4) | 
 
| isosceles_triangle(i,1,-3*pi/4,C) | 
 
| normal(affix(C)) | 
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